Recently, there is an increasing need to form a minute insulating region in various types of electronic devices. In a TSV (through-silicon-via) technology, for example, a through-electrode has to be electrically insulated from a silicon substrate. As means for electrical insulation, Japanese Unexamined Patent Application Publication No. 2008-251964 discloses a technology of forming a ring-shaped isolation groove passing through a silicon substrate in such a manner as to surround a through-electrode, forming a silicon film directly on the bottom and the side walls of the isolation groove, then forming an insulating film on the silicon film in such a manner as to fill up a gap left in the isolation groove, and thermally oxidizing each surface of the silicon film in contact with the inner or outer side wall of the isolation groove into a thermal silicon oxide film.
However, it is difficult to form a sufficiently thick insulating film, so that a metallic component of the through-electrode, e.g., Cu may be spread into the silicon oxide film and then into the silicon substrate, impairing the electrical insulation.
On the other hand, Japanese Unexamined Patent Application Publication No. 2004-31923 discloses the details of how an isolation trench groove should be formed for a MOS transistor or a bipolar transistor. Its disclosure is generally as follows.
(a) A suspension in which insulating particles such as silica particles are dispersed in a dispersion medium such as an organic solvent is applied to a trench-having surface of a silicon substrate by spin coating, and then, the dispersion medium is removed from the applied film to fill the trench with the insulating particles. The insulating particles are bonded neither to each other nor to the side walls and the bottom of the trench. Then, therefore, the upper side of the trench is closed by a reflowable dielectric layer, preventing the insulating particles from escaping from the trench.(b) Also disclosed is a particulate insulating layer in which after the insulating particles are filled in the trench in the same manner as in the above (a), the insulating particles are bonded to each other through an insulating binder to form a network structure of the insulating particles and the insulating binder. It describes that an inorganic or organic SOG obtained by dissolving a silanol in an organic solvent can be used as a material for the insulating binder. Also disclosed is that —OH and —O— bonded to an Si atom in the silanol used for the inorganic or organic SOG can be partially replaced with —H, that —CH3 in the silanol used for the organic SOG can be replaced with other alkyl groups such as —C2H5, that —OH and —O— bonded to an Si atom in the silanol used for the organic SOG can be partially replaced with alkyl groups such as —CH3 and —C2H5, and so on.(c) A first particulate insulating layer containing no binder and a second particulate insulating layer containing a binder are combined into an insulating layer. The top of the first particulate insulating layer containing no binder is covered with the second particulate insulating layer containing an insulating binder.(d) A particulate insulating layer forming an insulating layer includes first and second insulating particles that are homogeneously mixed together and an insulating binder for cross-linking them.
In Japanese Unexamined Patent Application Publication No. 2004-31923, however, since the insulating particles such as silica particles are bonded neither to each other nor to the side walls and the bottom of the trench, it is required to employ the technique of closing the upper side of the trench with a reflowable dielectric layer (see the above (a)) or the technique of bonding the insulating particles through a binder (see the above (b) to (d)), complicating the insulating structure and the manufacturing process.
In the case of the above technique (a), moreover, it is impossible to form an insulating layer having a high adhesion strength to the silicon substrate. In the case of the technique (b), since the particulate insulating layer has a network structure composed of the insulating particles and the insulating binder, the adhesion strength of the insulating layer to the silicon substrate is not sufficient, either. When using a binder such as an organic SOG, on the other hand, since the insulating layer contains carbon, it is not inherently desirable as an insulating layer that requires high insulation resistance. In the techniques (c) and (d), since the first and second insulating particles are employed, the problem still remains regarding the adhesion strength.
Furthermore, when the binder for bonding the insulating particles together is filled and hardened after the insulating particles are put in the trench, the whole body may shrink to leave a gap between the insulating layer and the substrate.
Meanwhile, Japanese Unexamined Patent Application Publication No. 2010-132511 discloses a technology in which a SIRAGUSITAL-B4373 (heatless glass) silica liquid in which inorganic compound particles of a submicron size are dispersed and filled is coated on an interface between a glass and a glass or a metal or between a metal and a metal or a ceramic and a vitrified networking reaction is allowed to proceed to complete vitrification hardening.
Also in this technology, however, when the insulating particles are hardened in a minute space, the whole body may shrink to leave a gap between the insulating layer and the substrate.